Golf club

ABSTRACT

A high performance golf club is provided at low cost, in which the thickness of a face portion is thinned and a sweet area is widened to enhance resilience to golf balls. In a golf club with a shaft  2  connected to a head  1,  the head  1  is provided with a face  3  portion on a front face and a shaft connecting portion  8  on one side, in which at least the face portion  3  is formed from spring steel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a golf club.

[0003] 2. Description of the Related Art

[0004] Hitherto, low carbon steel such as S20C (carbon steel for mechanical structure), that is, so-called soft iron, is in wide use as an iron-based material for golf club heads. If golf club heads are manufactured by a forging process using such soft iron, there can be obtained golf clubs giving such a good feeling at the time of striking golf balls.

[0005] On the other hand, it is generally known that the thinning of a face is effective in order to enlarge a sweet area which is a certain area on a face that realizes comparatively long carry of golf balls when balls are struck thereon, or to enhance the repulsive force to golf balls. However, as golf clubs made of soft iron have such a low durability of the material itself against strikes by golf balls, the thinning of a face causes dents on a surface of the face by repeated strikes by golf balls. Accordingly, there has been a lower limit of about 3.0 mm in the thickness of a face.

[0006] A conventional technique to thin a face, overcoming such drawback is disclosed in Japanese Un-Examined patent publication No.7-308410, in which marageing steel is used as a material for constituting a face. Since marageing steel has extremely high strength, the use of maragening steel enables a face to be thinner than that in the prior art. However, marageing steel contains as much as 30% or more additive elements, so that it is an extremely expensive material, thus leading to a drawback that the use of the material results in golf club products becoming too expensive.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to solve the abovementioned problems, providing a high performance golf club, at low cost, with a thinned face portion, a widened sweet area and high resilience to golf balls.

[0008] According to a first aspect of the invention there is provided a golf club with a shaft connected to a head provided with a face portion on a front face and a shaft connecting portion on one side, wherein at least said face portion is formed from spring steel.

[0009] According to the construction of the first aspect, a high performance golf club can be provided at a low price, wherein the face portion can be thin due to excellence of spring steel in fatigue strength and further spring steel has a low price due to a small quantity of additional elements so that a sweet area can be widened to enhance resilience to golf balls.

[0010] The invention according to a second aspect is a golf club according to the first aspect, wherein thickness of said face portion is 2.5 mm or less.

[0011] According to the construction of the second aspect, a high performance golf club can be provided, wherein a sweet area can be widened to enhance resilience to golf balls.

[0012] The invention according to a third aspect is a golf club according to the first or the second aspect: wherein a recess portion is formed on a rear side of said head and said head comprises, a head body forming a window hole in a front face thereof corresponding to said face portion so as to connect the window hole to said recess portion, and a face member firmly fixed to said window hole, while an undercut portion is formed on said face portion side of an lower inner surface of said recess portion.

[0013] According to the construction of the third aspect, a high performance golf club can be provided, wherein a sweet area can be widened and resilience can be enhanced by effective deflection of the face portion due to elimination of metallic parts from a near portion to the face portion.

[0014] The invention according to a fourth aspect is a golf club according to the first or the second aspect, wherein a rear shell is formed at a rear side of said head via a hollow portion and said head comprises, a head body forming a window hole in a front face thereof corresponding to said face portion so as to connect the window hole to said hollow portion, and a face member firmly fixed to said window hole, while an undercut portion is formed on said face portion side of an lower inner surface of said hollow portion.

[0015] According to the construction of the fourth aspect, a high performance golf club can be provided, wherein a sweet area can be widened and resilience to golf balls can be enhanced by effective deflection of the face portion due to elimination of metallic parts from near portions to the face portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a more complete understanding of the present invention, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0017]FIG. 1 is a front view illustrating a first embodiment of the present invention.

[0018]FIG. 2 is a cross-sectional view illustrating the first embodiment of the present invention.

[0019]FIG. 3 is an exploded front perspective view illustrating the first embodiment of the present invention.

[0020]FIG. 4 is an exploded roar perspective view illustrating the first embodiment of the present invention.

[0021]FIG. 5 is a perspective view showing a golf club at the time of machining according to the first embodiment of the present invention.

[0022]FIG. 6a is a cross-sectional view showing a golf club at the time of welding, while FIG. 6b a partially enlarged section thereof according to the first embodiment of the present invention

[0023]FIG. 7 is a cross-sectional view illustrating a second embodiment of the present invention

[0024]FIG. 8 is a cross-sectional view illustrating a third embodiment of the present invention

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereunder is a description of embodiments of the present invention with reference to the accompanying drawings. FIG. 1 to FIG. 6 show an iron type golf club that is a first embodiment, which is provided with a head 1 and a shaft 2. The head 1 is, on a front face thereof, formed with a face 3, that is a face portion for striking golf balls (not shown in the drawings), while a top 4 on an upper portion of the face 3, a sole 5 on a lower portion thereof, a toe 6 on one side, and a heel 7 on the other side of the face 3 are formed, respectively. Further, a shaft connecting portion 8 referred to as a hose) or the like is protruded obliquely upwardly on the upper portion of the heel 7, while a lower end of the shaft 2 is connected to the shaft connecting portion 8.

[0026] Further, a recess portion 9 is formed in order to enhance moment of inertia by distributing weight on the peripheral portion of a rear side of the head 1. This recess portion 9 is formed with a bottom surface 9A opposing the face 3, an upper inner surface 9B on an upper portion, a lower inner surface 9C on a lower portion, a first side inner surface 9D on one side and a second side inner surface 9E on the other side. Further, in the drawing, numeral 10 denotes lateral grooves called score lines or the like formed on the face 3.

[0027] The head 1 comprises: a head body 1A including the aforesaid shaft connecting portion 8 on the other side and a window hole 11 on a front face thereof corresponding to the face 3, said window hole 11 extending to communicate with the bottom surface 9A of the recess portion 9; and a face plate 14 or a face member, fixed firmly to this window hole 11. A peripheral portion 12 of the window hole 11 is arranged via a step portion 13 more outside than the upper inner surface 9B, the lower inner surface 9C, the first side inner surface 9D and the second side inner surface 9E, of the bottom surface 9A. Further, the face plate 14 is firmly fitted into the window hole 11 with the rear surface thereof being abutted against the bottom face 15 of the step 13. Moreover, a depressed portion 16, that is an undercut portion, is formed on the face 3 side on the lower inner surface 9C of the recess portion 9 which forms a cavity. This depressed portion 16 is depressed toward the sole 5 and formed from the first side inner surface 9D to the second side inner surface 9E on the lower inner surface 9C. The depth D of the portion 16, that is, a distance D between the deepest surface of the depressed portion 16 and the lower inner surface 9C is set at 7 mm or more, preferably at 10 mm or more. In the meantime, this depressed portion 16 is aimed at deepening the center of gravity of the head, enlarging a sweet area, and making it easier to raise golf balls, and further allowing the face 3 to be deflected efficiently by removing metallic parts from near the face 3.

[0028] It should be noted herein that the head body 1A is formed from S20C that is low carbon steel by forging, using a metal mold. The face plate 14 is formed to a thickness of 2.5 mm by applying blank processing (contour punching processing) to spring steel, i.e., rolled steel plate of 2.5 mm thickness. It is preferable that the thickness of the face plate 14 is as thin as possible as the sweet area can be widened. As a result of an experiment, however, it has turned out that when the thickness of the face plate 14 is made lass than 15 mm, even the comparatively small number of times of strikes causes depression on the face plate 14. Further, it has turned out that the thickness of the face plate 14 should preferably be 2.0 mm or more in order to insure strength against repeated strikes. On the other hand, if the thickness of the face plate 14 is more than 3.0 mm, it brings about little or no effect to widen the sweet area, and thus it is not preferable. However, when it is 2.5 mm or less, marked effect to widen the sweet area has been noted. Consequently, the thickness of the face plate 14 may be specified as 3.0 mm or less, preferably as 1.5 to 2.5 mm, more preferably as 2.0 to 2.5 mm. The thickness of the face plate 14 may be varied according to the thickness of rolled steel plate of SUP 10 used for the face plate 14. Incidentally, the face plate 14 may be formed by forging.

[0029] Whilst spring steel is given a notation of SUP in JIS standard, it is an abbreviation for Steel Use Spring. The kinds, chemical composition and mechanical properties of spring steel are as shown in Tables 1 and 2. Any kind of the listed spring steel contains as less as 5% or less additive elements, and thus it is inexpensive.

[0030] SUP 10 used in the present embodiment is used as a coil spring or the like, having such a mechanical strength that proof stress is 1,079N/mm² or more, tensile strength 1,226N/mm² or more, and hardness (HD) 363 to 429 by JIS standard. On the other hand, although not shown in tables, S20C has such a mechanical strength that yield point is 245N/mm² or more, tensile strength 400N/mm² or more, and hardness (HB) 116 to 174 by JIS standard. Consequently, mechanical strength of S20C is considerably lower than that of SUP 10. TABLE 1 Chemical Composition of Spring Steel (JIS G4801) JIS Chemical Composition (%) Symbol C Si Mn P S Cu Cr Mo V B SUP3 0.75-0.90 0.15-0.35 0.30-0.60 0.035 0.035 0.30 — — — — or less or less or less SUP6 0.56-0.64 1.50-1.80 0.70-1.00 0.035 0.035 0.30 — — — — or less or less or less SUP7 0.56-0.64 1.80-2.20 0.70-1.00 0.035 0.035 0.30 — — — — or less or less or less SUP9 0.52-0.60 0.15-0.35 0.65-0.95 0.035 0.035 0.30 0.45-0.95 — — — or less orless or less SUP9A 0.56-0.64 0.15-0.35 0.70-1.00 0.035 0.035 0.30 0.70-1.00 — — — or less or less or less SUP10 0.47-0.55 0.15-0.35 0.65-0.95 0.035 0.035 0.30 0.80-1.10 — 0.15-0.25 — or less or less or less SUP11A 0.56-0.64 0.15-0.35 0.70-1.00 0.350 0.035 0.30 0.70-1.00 — — 0.0005 or less or less or less or less SUP12 0.51-0.59 1.20-1.60 0.60-0.90 0.035 0.035 0.30 0.60-0.90 — — — or less or less or less SUP13 0.56-0.64 0.15-0.35 0.70-1.00 0.35 0.035 0.30 0.70-0.90 0.25-0.35 — — or less or less or less

[0031] TABLE 2 Mechanical properties of Spring Steel (JIS G4801) Mechanical Properties Proof Elongation Reduction Stress Tensile % of Area % JIS Thermal Treatment(° C.) 0.2% Strength No 4 or No 7 No 4 Hardness Symbol Quenching Tempering N/mm² N/mm² Test Piece Test Piece (HB) Example SUP3 830-860 450-500  834 1079 8 or more — 341-401 Leaf Oil-Cooling or more or more Spring SUP6 830-860 480-530 1079 1226 9 or more 20 363-429 Leaf Oil-Cooling or more or more or more Spring, SUP7 830-860 490-540 1079 1226 9 or more 20 363-429 Coil Oil-Cooling or more or more or more Spring SUP9 830-860 460-510 1079 1226 9 or more 20 363-429 Oil-Cooling or more or more or more SUP9A 830-860 460-520 1079 1226 9 or more 20 363-429 Concrete Oil-Cooling or more or more or more Ball SUP10 830-860 470-540 1079 1226 10 or more  30 363-429 Coil Oil-Cooling or more or more or more Spring SUP11A 830-860 460-520 1079 1226 9 or more 20 363-429 Leaf Oil-Cooling or more or more or more Spring, Coil Spring SUP12 830-860 510-570 1079 1226 9 or more 20 363-429 Coil Oil-Cooling or more or more or more Spring SUP13 830-860 510-570 1079 1226 10 or more  31 363-429 Large Oil-Cooling or more or more or more Leaf Spring, Coil Spring

[0032] Next is a description of a method for manufacturing a golf club of the present embodiment. First, a prototype (not shown in the drawings) of the head body 1A is formed from a metallic raw material (not shown in the drawings) of low carbon steel S20C by forging, using a metal mold. Thereafter, as shown in FIG. 5, the recess portion 9, window hole 11 and depressed portion 16 are processed to be formed by machining tools 20 such as cutting or grinding tools, including an end mill and a turning tool. The depressed portion 16 is formed by cutting or grinding the front side of the lower inner surface 9C with the machining tool 20 to be put into the window hole 11 from a front side of a face. Further, a small convex portion 18 is formed overall or partially along the peripheral portion 12 of the window hole 11, that is, on the top 4 and the sole 5 sides along the peripheral portion 12 in the present embodiment. A height X of this convex portion 18 is 1 mm or less, preferably about 0.8 mm, and a width Y thereof is 1 mm or less, preferably 0.5 mm.

[0033] On the other hand, spring steel SUP 10 of 2.5 mm thickness rolled steel plate is formed into a shape of the face plate 14 through blank process (contour punching process). Then, a chamfered portion 19 is formed on a fringe of a rear portion of the face plate 14 so that an air gap 22 with a triangle profile, as shown in the partially enlarged cross sectional view of FIG. 6, is formed such that an angle of the bottom surface 10 to the chamfered surface may be 45 degrees or more, for example, 80 degrees and the upper side of the triangle may be in the order of 0.5 to 1.5 mm in length.

[0034] Thereafter, the head body 1A and the face plate 14 are firmly fixed together by laser welding. After the face plate 14 is fitted into the window hole 11 of the head body 1A, laser welding is applied with a head 21 of a laser welder being pointed to the peripheral portion 12 of the window hole 11. At this time, the convex portion 18 is also fused while the welded center portion is raised but both sides thereof sink to form depressed areas. However, as the fused metal of the convex portion 18 flows into the depressed areas so that the depressed areas can be prevented from occurring. In the meantime, whilst the convex portion 18 has height X of 1 mm or less and width Y of 1 mm or less, laser is likely to go out of focus if larger dimensions than these dimensions are employed, thus leading to a possibility that the convex portion 18 cannot be melted well.

[0035] While welding is being performed by applying laser beam from a front side, the air gap 22 is formed between the face plate 14 and the bottom portion 15 by the chamfered portion 19 formed in a rear portion of the face plate 14, so that the face plate 14 has a partially thinned portion. By applying penetration welding to the partially thinned portion, clearance is insured for air bubbles generated during the laser welding to go out therethrough. In this case, air bubbles are not confined to the welded portion so that no pin hole is formed in the welded portion. Laser welding should have a specification such that an output is 450 W, welding speed 250 mm/minute, the number of pulses 30 pps, and depth of penetration in the order of about 1.5 to 1.6 mm. In the meantime, the chamfered portion 19 will do as long as the air gap 22 is formed, and thus a shape and angle of the chamfer may be varied.

[0036] Laser welding used here is advantageous in that it brings about fewer portions influenced by heat to produce fewer distortions than TIG welding, enabling the welding between different metals, requiring no weld rods so that the automation of welding is possible, using automating programming, and that a welding portion is V-shaped so that good welding can be performed. Moreover, as laser beams are electromagnetic waves, the working environment is not subject to restrictions, and laser beams can be condensed and changed in its course by optical apparatuses (lenses or mirrors), without constraints of machining jigs as laser beams are not affected by electromagnetic fields, enabling the welding of both metals and nonmetals, with no X ray being emitted from raw materials. In this respect, electron beam welding needs vacuum environment in general, having disadvantages for facilities and workability. TIG welding bas drawbacks that a number of distortions take place due to great thermal influence, time-consuming due to manual procedure and bead lines are unstable.

[0037] Thereafter, thermal treatments of quenching and tempering are applied to the head 1, whose strength and toughness are thermally adjusted, while further grinding and plating or the like are applied to finish the head 1.

[0038] Shot peening may be applied to spring steel in order to enhance its fatigue strength further where such treatment is suitable, provided that attention is paid not to cause deflection in the face plate 14 as it is likely to be deflected by the stress developed at the time of shot peening due to the thinness of the face plate 14 in the present embodiment.

[0039] As described above, a golf club of the foregoing embodiment is a golf club including: the head 1 with the face 3 on a front and the shaft connecting portion 8 on one side; and the shaft 2 connected to the head 1, wherein at least said face 3 is formed from spring steel. Consequently, the face 3 is not dented by repeated strikes against golf balls due to the excellent fatigue strength of spring steel even if the face 3 is made thin. Accordingly, it is possible to make the face 3 thin, and there call be provided a high performance golf club at a low price bit enlarging a sweet area and enhancing resilience of the face to golf balls owing to spring steel containing such a small quantity of additive elements that it is inexpensive.

[0040] According to the second aspect of the invention, as the thickness of said face 3 is made 2.5 mm or less, a high performance golf club can be provided, with an enlarged sweet area and enhanced resilience to golf balls.

[0041] Moreover, according to the third aspect, the recess portion 9 is formed on a rear side of said head 1, said head 1 comprising: the head body 1A including the window hole 11 an a front face thereof, corresponding to the face 3, said window hole 11 extending to communicate with the recess portion 9; the face plate 14 fixed firmly to this window hole 11;and the depressed portion 16 as an undercut portion formed on the face 3 side on the lower inner surface 9C of the recess portion 9 Accordingly, there can be provided a high performance golf club with an enlarged sweet area as well as the enhanced resilience to golf balls by removing metallic parts from near the face 3.

[0042] Next is a description of a second embodiment with reference to FIG. 7. The same reference symbols are used for parts the same as in the first embodiment, and detailed description thereof is omitted, FIG. 7 shows a hollow iron type or wood type golf club of the second embodiment of the invention. The construction of the second embodiment is totally the same as the first embodiment expect that a rear shell 42 is integrated with a rear side of a head body 1 via a hollow portion 41.

[0043] According to the second embodiment of the inventions, which corresponds to the fourth aspect of the invention, the rear shell 42 is formed in a rear side of said head 1 via the hollow portion 41, said head 1 comprising: the head body 1A including the window hole 11 on a front face thereof, corresponding to the face 3, said window hole 11 extending to communicate with the hollow portion 41; the face plate 14 fixed firmly to this window hole 11;and the depressed portion 16 as an undercut portion formed on the face 3 side on the lower inner surface 9C of the hollow portion 41. Accordingly, there can be provided a high performance golf club with an enlarged sweet area as well as the enhanced resilience to golf balls by removing metallic parts from near the face 3.

[0044] Next is a description of a third embodiment with reference to FIG. 8. The same reference symbols are used for parts the same as in the first embodiment and detailed description thereof is omitted. FIG. 8 shows a wood type golf club as the third embodiment. A head 1 is a so-called metal wood that is made of metal and hollow. The head 1 has a hollow portion 51 thereinside, in which filling material such as polyurethane or the like may be filled. The head 1 is constructed of three pieces, for example. That is, the outer shell of the bead 1 comprises the face plate 14 that is a tabular face member, a body member 52 and a crown member 53. The face plate 14 forms the face 3, the crown member 53 forms the top 4 and the body member 52 forms the sole 5 or the like other than the formers. Further, the face plate 14, the body member 52 and the crown member 53 are joined together by means of welding or the like.

[0045] Further, the face plate 14, the body member 52 and the crown member 53 are formed from rolled steel plate of SUP 10 that are spring steel, through forging or press molding. The thickness t1 of the face plate 14 is 2.5 mm and the thickness t2 and t3 of the body member 52 and the crown member 53 are formed thinner than the thickness t1 of the face plate 14. As the preferable thickness of the face 14 is the same as in the first embodiment, the description thereof is omitted. Moreover, only the face plate 14 may be formed from spring steel and the other members may be formed from titanium-based alloy or low carbon steel or the like.

[0046] Incidentally, the present invention should not be limited to the aforementioned embodiments but a variety of modifications are possible within the scope of the present invention.

[0047] Whilst the aforementioned embodiments are described by taking an iron type, a hollow iron type or a wood type golf club as examples, the present invention should not be limited to these types, but may be applied to a putter as well.

[0048] Further, although only the face member is formed from spring steel in the first and second embodiments, the whole of the head 1 may be fabricated by forging, using spring steel. Further, spring steel should not be limited to SUP 10 but other kinds of spring steel may be used. Additionally, when forming the head 1 from the face member 14 and the head body 1A, the material of the head body 1A should not be limited to S20C but may be other kinds of iron-based materials, stainless steel and titanium alloys or the like. Moreover, joint method between the face member 14 and the head body 1A shall not be limited to laser welding but may be other welding means such as TIG welding, press-fitting or fitting through plastic deformation of materials, or bonding with an adhesive. Alternatively, the window hole 11 and the depressed portion 16 may be formed not by cutting or grinding but by forging at the same time when the head body 1A is fabricated by forging. In addition, although the small convex portion 18 is formed along the peripheral portion 12 on the top 4 and the sole 5 side of the head body 1A in the foregoing embodiments, the position of the convex portion 18 should not be limited to there but may be any other suitable position in the peripheral portion 12, or otherwise, it may be formed on a whole or partial peripheral portion of the face member 14. 

What is claimed is:
 1. A golf club with a shaft connected to a head provided with a face portion on a front face and a shaft connecting portion on one side, wherein at least said face portion is formed from spring steel.
 2. A golf club according to claim 1, wherein the thickness of said face portion is 2.5 mm or less.
 3. A golf club according to claim 1, further comprising a recess portion formed on a rear side of said head, and wherein said head comprises: a head body including a window hole on a front face thereof, corresponding to said face portion, said window hole extending to communicate with the recess portion; a face plate fixed firmly to this window hole; is and a depressed portion as an undercut portion formed on the face side on a lower inner surface of the recess portion
 4. A golf club according to claim 2, further comprising a recess portion formed on a roar side of said heads and wherein said head comprises: a head body including a window hole on a front face thereof, corresponding to said face portion, said window hole extending to communicate with the recess portion; a face plate fixed firmly to this window hole; and a depressed portion as an undercut portion formed on the face side on a lower inner surface of the recess portion.
 5. A golf club according to claim 1, further comprising a rear shell formed on a rear side of said head via a hollow portion, wherein said head comprises: a head body including a window hole on a front face thereof, corresponding to the face portion, said window hole extending to communicate with the hollow portion; a face plate fixed firmly to this window hole; and a depressed portion as an undercut portion formed on the face side on a lower inner surface of the hollow portion.
 6. A golf club according to claim 2, further comprising a rear shell formed on a rear side of said head via a hollow portion, wherein said head comprises: a head body including a window hole on a front face thereof, corresponding to the face portion, said window hole extending to communicate with the hollow portion; a face plate fixed firmly to this window hole; and a depressed portion as an undercut portion formed on the face side on a lower inner surface of the hollow portion. 